The application proposes research on virus structure and assembly. The mechanism by which DNA is packaged within the viral capsid, and the structure of this condensed DNA will be studied. How the DNA packaging mechanism interacts with viral DNA metabolism, specifically DNA repair and recombination processes, in the infected cell will be studied in vitro in an extract which displays both DNA packaging and recombination. Electron microscopy will be used to study in vivo the process fo DNA packaging, viral assembly, and DNA structure, as well as the consequences for viral DNA packaging of lesions in duplex DNA structure. A head assembly related DNA dependent ATPase-endonuclease purified from the viral infected cell will be examined for its effect upon DNA structure and its role in the DNA packaging process. Other viral gene products known to be involved in linking DNA to the provirus structure will be lpurified, and their binding specificity to DNA and to the DNA entrance vertex structural protein of the capsid will be determined. Viral DNA metabolism gene products involved early in infection in DNA synthesis will be examined for their involvement in in vitro recombination in the cellfree viral infected extract system. Early stages in viral capsid formation will be studied, with particular emphasis upon the energetics of capsid shell formation and head expansion as determined by microcalorimetry. The basis for mutants which overproduce certain viral DNA packaging gene products will be determined. If, as preliminary evidence has led us to propose, some viral DNA packaging occurs by an enzymatic process, this step might be subject to viral specific inhibition. Knowledge about these processes will shed light upon DNA condensation, movement, and metabolism in virus infected and normal cells, and is a model for eucaryotic chromosome condensation.